This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Magnetotactic bacteria occur naturally and produce chains of magnetite particles, which allow them to align along the Earth's geomagnetic field lines. The magnetite particles are similar to existing iron oxide particles used extensively as contrast agents for MRI enhancement. Due to the microaerophilic nature of magnetotactic bacteria, we reasoned that they may preferentially colonize cancerous tumors, enabling their visualization in vivo using MRI. Although certain bacteria have been known to preferentially colonize cancerous tumors for over 50 years, only recent advances in our understanding of, and ability to manipulate bacteria, have led to a renewed interest in their use for treating cancer.